- An algorithm is presented for identifying critical generators and loads in power systems with voltage problems. It is based on sensitivity analysis of generated reactive powers with respect to load requirements. System loading based on a small number of independent parameters and an algorithm for identifying critical single-line outages based on the information from sensitivity analysis are proposed. The algorithm was tested on a 39-bus system. The method does not guarantee that the outages critical for the transfer of active powers will be identified, but it identifies those outages which may result in severe voltage problems in a heavily loaded system.